| 摘要 |
Points for calculation are set at uniform intervals on an ideal lattice set over a pattern area on a reticle. An amount of light incident on a slit-shaped illumination area on a lens is measured with an integrator sensor. An amount of heat absorbed by the reticle according to the position in a scanning direction is calculated on the basis of a pattern presence ratio on the reticle, and an amount of thermal expansion at each point for calculation is calculated on the basis of the calculated amount of heat absorbed. A change in the magnification of a projected image is obtained from the calculated amount of thermal expansion. At the same time, a change in the projection magnification caused by a projection optical system itself is also calculated according to the position in the scanning direction of the reticle. The projection magnification of the projection optical system is corrected through a magnification correction mechanism so as to cancel both the magnification changes thus calculated.
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